This invention relates to a method of producing ceramics material, and more particularly, to a method for producing lithium aluminosilicate (LAS) ceramics.
Recently the performance of the precision device and the instrument equipment in high-tech system is limited by the problem of thermal expansion. To avoid this problem, it is required to develop the negative thermal expansion material to compose them into an athermal device so that the original device performance is maintained without being influenced by the variation of ambient temperature. For example, the fiber Bragg grating (FBG) device had composed the negative thermal expansion material with optic fiber to reduce the influence of the temperature on the index of refraction in the grating. It is known that the LAS ceramics with xcex2-eucryptite structure has been successfully used in FBG system. Besides, such technology also could be applied into the high-speed rotor of the CNC machine for thermal compensation. So it has been needed to develop the suitable fabrication process of negative thermal expansion ceramics with more uniform properties and stable structure.
The main compounds of the LAS system are xcex2-eucryptite (LiAlSiO4) with negative expansion, Spodumene (LiAlSi2O6) with almost zero expansion, and Petalite (LiAiSi4O10). In which, the thermal expansion coefficient (CTE) of sintered anisotropy xcex2-eucryptite ceramics are about xe2x88x928xc3x9710xe2x88x926/xc2x0 C., and they also have the advantages such as high mechanical strength, strong chemical corrosion-resistance and thermal-shock resistance, as well as fine size stability.
It is disclosed in many articles about the manufacturing method of the LAS ceramics. U.S. Pat. No. 6,087,280 discloses the method of manufacturing LAS ceramic material uses a melting glass-ceramic process including heat-treatment for controlling crystallization. However this method may result in different crystallizations with phase-separation and generate large thermal stress during the quenching process. Another, the negative-expansion ceramics substrate of the xcex2-quartz using the sinter method is disclosed by A. Sakamoto, wherein the coefficient of thermal expansion is adjusted by changing the difference between each ratio of the components. Even so, there is no refer to the calcinations of the precursor and the heat treatment after sintering. Besides, U.S. Pat. No. 6,066,585 discloses that the powder calcined temperature is 1000xc2x0 C.xcx9c1100xc2x0 C. whereas the sinter temperature is 1200xc2x0 C.xcx9c1300xc2x0 C., which could transform fully the crystal phase from the low-temperature phase into the xcex2-eucryptite (LiAlSiO4) with high temperature. However, it emphasizes the improved mechanical properties by adjusting the stoichiometric composition of Li1+xAlSiO4+x/2, and no refer to the microstructure of ceramics with stable properties and the proper heat treatment. Therefore, it has been needed to develop the method of manufacturing LAS ceramic substrates in order to obtain the better structure and quality of ceramics.
To achieve these and other advantages and in order to overcome the disadvantages of conventional methods in accordance with the purpose of the invention as embodied and broadly described herein, the present invention an improved manufacturing method for producing LAS ceramics.
In view of this, an object of the present invention is to provide a manufacturing method for LAS ceramics, which have uniform and stable thermal expansion coefficients, a more linear expansion curve, and a denser and more stable structure.
The present invention provides a manufacturing method for LAS ceramics. The method mixes lithium carbonate, aluminum oxide, and silicon oxide as a raw material powder. After mixing by ball-milling and drying the raw material powder, a calcinations process forms a precursor from the raw material powder. Next, the precursor is pressed into a green ceramic. The high-heat-conducting metal sheets are adhered tightly on both the upper and below surfaces of the green ceramic. The high-heat-conducting metal sheet material is a metal with a conducting coefficient higher than 10 W/mK. Next, a sintering process processes the green ceramic into ceramic. Finally, a heat-treatment process is performed.
The method of the present invention manufactures LAS ceramics utilizing a solid-state sintering method. During the heating processes, including the sinter process and the heat-treatment process, the high-heat-conducting metal sheets help to ensure uniformity of the ceramics in the temperature gradient. The high-heat-conducting metal sheet should be tightly adhered to the ceramics to ensure uniformity of the heat transfer. Additionally, after the sinter process, a heat treatment process is used to improve the heat-expansion hysteresis and thermal instability of the ceramics.
The present invention synthesizes the LAS ceramics using powders of lithium carbonate, aluminum oxide, and silicon oxide. In certain cases, problems of oxide corrosion or ceramics corrosion caused by lithium carbonate in a high-temperature reaction can result. However, the present invention performs a calcinations process to make the precursor from the raw material powders before the sintering process. Therefore oxide or ceramics corrosion during high temperature is prevented and the sinter process of the ceramics is successfully completed.
Additionally, the present invention utilizes the high-heat-conducting metals tightly attached to the top and bottom surfaces of the green ceramic during the sintering process, which allows for a more uniform heat transfer on the ceramic. In this way, the grains of ceramic are uniformly heated and treated during the sinter process, which lowers the aggregate effects of the anisotropic ceramic crystals so that the whole grains of ceramic crystal are more randomly arranged and distributed. Also, the subsequent heat-treatment process provides recovery and re-growing between the grains and forms the ceramics with a denser as well as a more stable structure.
The present invention further provides a manufacture method of ceramics material. After providing a precursor, the precursor is pressed into a green ceramic. The high-heat-conducting metal sheets are tightly attached, for example by pasting, on both the upper and below surfaces of the ceramic. Next, a sinter process is performed forming the green ceramic into ceramic. Then, a heat-treatment process is performed.
The precursor is provided by using a mixing powder with at least one component as a raw material powder. After mixing and milling and drying the raw material powders, a calcinations process is performed on the raw material powders so that the raw material powders form the precursor.
The present invention produces the ceramic material utilizing a solid state sintering method. A high heat-conducting metal sheet acts as a cap during all the ceramic-heated process including the sinter process and the heat treatment process to ensure uniform heating. The high heat-conducting metal sheets are pasted tightly to the ceramics to make the heat transfer with uniform. Next, after the sinter process, a heat-treatment process is performed to improve the heat-expansion properties and thermal instability of the ceramics.
The method of the present invention uses the high-heat-conducting metal on the top and bottom of the ceramics during the sinter process of the ceramics, which allows more uniform heat transfer to the ceramic. Since the heat is uniformly transferred during the sinter process the aggregate effects of the anisotropic ceramic crystals are decreased, which makes the whole crystals more randomly arranged and distributed. Finally, the subsequent heat-treatment process makes the recovery and re-growth between the grains which form the ceramics, denser and with more stable structure.
These and other objectives of the present invention will become obvious to those of ordinary skill in the art after reading the following detailed description of preferred embodiments.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.